Apparatus for the preparation of filamentary material

ABSTRACT

Apparatus for the manufacture of linear condensation polymers of increased relative viscosity employing in combination a means for feeding pre-formed particulate polymeric material of lower viscosity to a heating means which heats the material to a temperature lower than its melting point and subsequently passing the heated particulate material to a melting means for melting the particulate material whereby the melted material can be extruded.

United States Patent 91 Simons ,;[111 3,753,661 51 Aug. 21, 1973 [75]inventor: Frank Holmes Simons, Matthews, N.C.

[73] Assignee: Fiber Industries, Inc., Charlotte,

[22] Filed: Feb. 8, 1971 [21] Appl. No.: 113,597

Related US. Application Data [63] Continuation of Ser. No. 857,257, July23, 1969,

abandoned.

[52] US. Cl 23/285, 425/143, 264/25, 264/85, 264/176 F, 23/308, 23/280,23/260, 23/283, 126/3435 A, 219/422 8/1952 Culpepper et al. 264/858/1941 Graves 264/85 Primary Examiner-James H. Tayman, Jr. Attorney-S.D. Murphy, l-l. M. Adrian, Jr. and Robert J. Blake [57] ABSTRACTApparatus for the manufacture of linear condensation polymers ofincreased relative viscosity employing in combination a means forfeeding pre-formed particulate polymeric material of lower viscosity toa heating 51 Int. Cl C08g 35/00 means which heats the material atemperature [58] Field of Search 23/308, 285, 283, than its meltingPoint and subsequently Passing the 215/260, 264/85, 176 425/174, 85heated particulate material to a melting means for melting theparticulate material whereby the melted [56] References Cited materialcan be extruded.

UNITED STATES PATENTS 3,335,115 8/1967 Ludewig 264/176 F 2 Claims, 1Drawing Figure H5 5 OUT ff 28 a INSUlATION HEATING 30 T ZONE EMPERATURECONTROLLERS I7 TO SPINNERETTE Patented Aug. 21, 1973 3,753,661

POLYMER CHIPS INSULATION HEATING 3o ZONE TEMPERATURE CONTROLLERS 'TOSPINNERETTE INVENTOR FRANK HOLMES SIMONS ATTORNEY APPARATUS FOR THEPREPARATION OF FILAMENTARY MATERIAL This application is a continuationof Ser. No. 857,257 filed July 23, 1969 and now abandoned, which is adivision of Ser. No. 621,868 filed March 9, 1967 now patent No.3,480,596.

This invention relates to an apparatus for the production of highmolecular weight polymers, especially those prepared bycondensation-type reactions, such as polyamides and polyesters. Moreparticularly, this invention relates to an apparatus for the productionof linear polycarbonamides of a type characterized by high molecularweight including those particularly useful in the formation of shapedarticles such as fibers and filaments. Even more specifically, itrelates to an improved apparatus for increasing the relative viscosityof linear polyamides derived from dibasic acids and diamines.

An apparatus for practicing the above process includes in combination anelongated tubular heater affixed to a conventional melter.

The synthetic linear polycarbonamides or polyamides to which thedescription of this invention is more particularly addressed are of thegeneral types as described in U.S. Pats. Nos. 2,071,250; 2,071,251;2,071,252; 2,071253 and 2,130,948. They are commonly referred to by thegeneric term nylon and are characterized by the presence of recurringcarbonamide groups as an integral part of the polymer chain, whichgroups are separated by 'at least two carbon atoms. They are furthercharacterized by high melting point, pronounced crystallinity, andinsolubility inmost solvents except mineral acids, formic acids andphenols. Upon hydrolysis with strong mineral acids, the polymers revertto the reactants from which they were formed.

Synthetic linear polyamides are of two general types, those which areobtained from the self-polymerization of amino acids such as6-amino-caproic acid, its amideforming derivative, for example,epsilon-caprolactam; and those which are formed by the condensation of adiamine with a dibasic acid or an amide-forming derivative thereof.Diamines which can be condensed with equimolecular proportions of anappropriate dibasic acid to yield synthetic linear polyamides may berepresented by the general formula Nl-I,(Cl-l. ,),,Nl-i in which n is aninteger of 2 or greater and preferably from 2 to 8. Suitable examplesare ethylenediamine, propylenediamine, tetramethylenediamine,pentamethylenediamine, hexamethylenediamine, octamethylenediamine anddecamethylenediamine. Suitable dibasic acid reactants are represented bythe general formula HOOCRCOOH in which R is a divalent hydrocarbonradical having a general length of at least two carbon atoms.Representative reactants of this type are sebacic acid, octadecanedioitacid, adipic adid, suberic acid, azelaic acid, undecanedioic acid,glutaric acid, pimelic acid, and tetradecanedioic acid. As has beenindicated, the amide-forming derivatives thereof may be substituted forthe diamine and-dibasic acid reactants. Thus, the carbamate and N-formylderivative may be used in lieu of the diamines, while the monoanddi-ester, the anhydride, the mono and di-amide, and the acid halide maybe substituted for the dibasic acid.

Nylon polymers, or superpolyamides capable of forming fibers and havingmolecular weights in excess of about 10,000, are conventionally preparedby a. melt-polymerization process involving the condensa: tion of asuitable diamine and dibasicjacidwith ordinary heating to liberatewater. Often it isadvantageous to isolate and purify the salt, theproduct resultingfrom the first stage of the polymerization reaction, asshown, for example, in U.S. Pat. No. 2,130,947, the salt being thenheated under controlled, conditions of temperatures and pressure, suchas is disclosed in- U.S. Pat. No. 2,289,774, to expel water. ofcondensation and effect polymerization.

At the beginning of the polymerization reaction, since such is acondensation reagtijon with the liberation of water, a large amount ofwater is evolved. Its ready removal from the reaction zone expedites thepolymerization reaction. Moreover a low water, content is advantageousbecause the reaction being an equilibrium one proceeds further, the lessthe amount of water present. The continuing liberation of water advancesthe polymerization reaction. Although polymerization is usually carriedout under an inert atmosphere, e.g., nitrogen, a nonsolvent diluent has.also been proposed as the inert environment for the reactants.

in general, since the above-mentioned. polymerization is a condensationreaction with the liberation of water the amount of water liberatedis anindex of the degree of polymerization, which canbe convertedintovmolecular weight or viscosity criteria. Simularlythe extent to whichpolymerization has proceeded can be estimated by other methods includingdetermination of molecular weight and relative viscosity. The intimaterelationship that exists between molecular weight andrelative viscosityof polyamides is well known and, moreover, is described in detail-byMark in Physical Chemistry of High Polymeric Systems, Vol. ll, interSciencesPublications Inc. (1940).

The relative viscosity of a polyamide is defined as the ratio of theviscosity of a solutionof given strength of the polyamide in a givensolvent to the viscosity of the solvent itself at the same presecribedtemperature. In the case of the relative viscosity values quoted inthis, specification the solvent employed is a percent by weight (solutesolution) aqueous solution of formic acid. The absolute viscosity of an8-.4 percent by weight (solute solution) solution of the polyamide, inthe above mentioned solvent is determined and the ratio of saidviscosity to the absolute viscosity of the solvent itself evaluated. Thetemperature employed for the determination of viscosities is 25 C. Inorder that a polyamide may be melt-spinnable into filaments it must havea relative viscosity ranging from at least about 25 to 55. The latterfigure is obtainedapproximately when the process of condensationpolymerization is conducted so far that at least 96 percent of thetheoretical total water of chemical condensation i.e., of the maxi.- mumwater theoretically available, is eliminated by the condensationreaction.

Whether the polycondensation reaction abovementioned is carried outbatchwise or continuously, conditions of polymerization are such thatreactants and polymer at the end of the reaction are in a moltencondition. Although widely used, melt polymerization is fraught withcertain disadvantages. Thus, as polymerization progresses, the viscosityof the melt increases, portions of the viscous mass oftengend to remainin a relatively stagnant or physically inert condition, particularly inthe latter stages of the pglycondensation process, and stirring becomesextremely difficult. The increasing viscosity of the molten mass tendsto inhibit the efficient performance of the polycondensation reaction inthat considerable difficulty is experienced in removing water from thereaction mass and the relative viscosity of the final polymer thereforebecomes limited. Moreover, because of the aforementioned problems, thisgives rise to poor heat transfer properties, as a result of which hightemperatures and long reaction times are required to effect evaporationof volatile products and to promote favorable completion of thepolycondensation reaction. Often undesirable side reactions occur withthe formation of thermal degradation products and/or gel thus resultingnot only in an inferior product, but necessitating shut-down forcleaning of equipment and maintenance. Even without formation ofdegradation products, however, the making of a high viscosity polymer inthe autoclave is undesirable because it requires relatively long periodsof time and because of the viscosity is difficult to discharge from theautoclave thus resulting in inefficient utilization of the autoclave,lowered productivity, and the like. In addition, as the process nearscompletion and the sytem pressures are reduced to flash off volatilematerial such as reaction water and like substances, excessive heat lossoccurs within the system. During the sudden reduction of pressure thereoccurs a violent splattering of the reaction mass on the walls and pipeswithin the system which further restricts the transfer of heat to thereaction mass and promotes the formation of clusters of obnoxiousmaterial heretofore mentioned and commonly referred to as gels. Althoughthe chemical composition of the gels is not understood precisely, it isknown that they are objectionable and cause a substantial reduction inthe quality of the polymeric end products as well as necessitatingequipment shutdowns for their cleaning and removal. Moreover, it isknown to be highly desirable to eliminate any gel formation because oftheir auto-catalytic nature. Finally, in melt polymerization it isnecessary to quench large masses of high viscosity molten polymer fromhigh to low temperatures. The reaction products cannot be rapidly cooleden masse, as a result of which portions of the reaction mass aresubjected to differences in temperature and time of reaction whereby togive materials of different degrees of polymerization and hence a finalproduct having an undesirable molecular weight range.

Numerous investigators have proposed a variety of processes of andapparatus for increasing the relative viscosities of polyamides, some ofwhich provide continuous operation, while others are merely to improvethe well-known batch or discontinuous polymerization process. Forexample, it is known that viscosity can be increased by equilibration ofthe molten polymer under vacuum, but unfortunately this is difficult andexpensive'to control in commercial practice. Moreover, because thepolymerization reaction is, as beforementioned a reversible reaction,this requires either immediate use of the polymer, as for example, inthe formation offilaments or desiccation of polymer chips during storageand their subsequent use. Of course immediate'use of the polymer in somemanufacturing operations is impossible because such requires specialequipment and handling. As is well known, desiccation is attendant withmany problems in addition to also requiring special equipment andhandling. Chips sealed in storage cans or the like often pick up varyingamounts of moisture thereby resulting in chips of varying relativeviscosity and polymer of non-uniform relative viscosity necessitatingsteaming of the chips as in U.S. Pat. No. 2,571,975. Other known methodsfor increasing polymer viscosity are by drying the polymer for extendedperiods of time at elevated temperatures in an inert atmosphere, or bythe addition of trifunctional reactants. Such drying, of course, becausethe chips are not immediately used requires desiccation and involves theproblems accompanying such as above-mentioned. In U.S. Pat. No.2,172,374 to Flory, the patentee discloses a process for increasing themolecular weight of a polyamide by heating polymer chips, said polymerhaving been formed by melt polymerization, at polyamide formingtemperatures and below the melting point of the chips until thepolyamide has undergone a substantial increase in intrinsic viscosity.British Patent 806,088 describes a process of preparing linearpolyamides of a relative viscosity of at least which comprises heatinggranular polyamide to a temperature of from 200 to 240 C, but below themelting point of the polyamide, while passing a dry inert gastherethrough and then stopping the treatment when the desired relativeviscosity has been attained by rapidly cooling the treated polyamide.Similarly, a so lid-state polymerization process is described in BritishPat. No. 802,970 and U.S. Pat. No. 3,031,433. In U.S. Pat. No. 2,865,895there is disclosed yet a different polyamide polymerization processconducted in two stages wherein after the first melt polymerization, asecond polymerization is conducted on solid polyamide particles in aliquid which is nondissolving and inert toward the polyamide, attemperatures below the melting point of the polyamide. A similar processis disclosed in U.S. Pat. No. 2,987,507.

While some of these processes and apparatuses offer definite advantages,others are either very costly, inefficient, difficult to control inpractice, or present serious processing disadvantages, such as thenecessitating of desiccation, solvent removal, and the like. A singulardisadvantage not mentioned above and possessed by all known batchpolymerization processes involves the inefficiency and expense resultingfrom the various heating and cooling cycles involved. For example, inall the known processes involving solid phase polymerization, thepolymer chips are heated, cooled, stored with des' iccation, and thenheated again to melt the polymer for use, such as the spinning intofilaments.

It has now been discovered in accordance with the present invention thatlinear condensation polymers of increased viscosity can be obtainedwithout the disadvantages of prior art processes and with apparatuswhich is relatively inexpensive and involves no complicated addition topresent equipment, either in design or operation.

OBJECTS OF THE INVENTION Accordingly, it isan object of this inventionto provide linear condensation polymers, particularly polyhexamethyleneadipamide of increased relative viscosity.

It is a further object to provide a novel apparatus combination by meansof which polymers of increased relative viscosity can be obtained bothsimply and efficiently.

It is an additional object to provide a simple apparatus for increasingthe relative viscosity of linear con- -which, the sole FIGURE thereof isa diagrammatical practicing the invention.

DETAILED DESCRIPTION OF THE INVENTIO Broadly the invention contemplatesproducing a linear condensationpolymer of increased relative viscositywhich comprises taking ordinary autoclave polymer in the form ofparticulate material, i.e., chips, heating the chips at a temperatureless than the melting point while passing a stream of inert gas over thechips, and immediately melting the chips in preparation forspinning.Upon melting the polymeric material rapidly conrepresentation of anembodiment of apparatus used in creased viscosity.

The inventionprocess described hereinafter with more particularity withrespect "topolyhexamethylene adipamide, i.e., nylon 66, issuperior topreviously used processes both from the standpoint of cost of productionand from the standpoint of uniform quality "of product. I"

The advantages of the present process are enhanced by reason of thefactthat itmay be carried out by a simple-apparatus addition to existingequipment.

7 Turning now to the drawing in which there is shown in the sole FIGUREthereof anapparatus for the practice of my invention comprising incombination a feed hopper l0, tube heater 11, and melter 12, theinvention will be described in greater detail.

Conventional polyamide chips having 'an ordinary autoclave relativeviscosity, hereinafter referred to for sake of brevity by RV, of 50 orless, preferably 48 or less and even more desirably, less than about 45are fed 'into feed hopper It), which supplies a feed of chips to tubeheater l1. Thepolymer chips containing about 1-1.5 percent watertherein, which includes both dissolved water of equilibrium at theparticular autoclave relative viscosity and water either absorbed oradsorbed are heated and dried in the tube and melter'12, as hereinaftermore fully'described. Heating the chips causes the water therein todiffuse to the surface of the chips whereby such can be removed bypassing a stream of inert gas, such as nitrogen, countercurrent to thechip flow, as is shown in the drawing. It is underdenses andequilibrates to a polymer having an insphere, as shown by the arrows inthe drawing, carrying trogen temperature.- The chips are heated anddried I until sufficient water has been removed therefrom to shift thepolymerization equilibrium upon melting to the desired relativeviscosity. Upon melting the polymerization reaction proceeds veryrapidly with the liberation of water to establish anew equilibrium, andthe polymer re-equilibrates in the melt pool at an increased viscositylevel which depending on the amount of water removed during drying maybe as much as 55, or even more.

. It is quite surprising that relative viscosity increases can beachieved in such a two step process. Especially it is surprisingthat-water can be removed first, i.e., be-

fore the condensation reaction occurs, at a relatively low temperature,and that the reaction is rapid enough to be'finished in the few minutesavailable in the melt.

This particularly advantageous in that there is less time for oxidationor other side effectsjto occur and in that it'permits theafter-polymerizationT and spinning to be onecontinuous operation.Contrary to other known condensation polymerization reactions, the

water of condensation is not removed but instead is used in the meltpool to determine and control the final relative viscosity or degree ofpolymerization.

Although it is primarily intended to heat the chips in tube 11 in orderto provide chips having less than their equilibrium water content tomelter 12, a small amount of polymerization on the order equivalent to1-2 RV units can be otained, if desired, in the solid phase durstood, ofcourse, by those skilled in the art that inert gases other than nitrogencan be-used, e.g., carbon dioxide, argon'or any of the like non-reactivegases. Nitrogen,'which is at room temperature, e.g. about 20 'C, orwhich may be heated to a temperature of about 170 C or more, as desired,is passed into chip melter, l2

through'inlet 44 and a circular manifold, not shown, but which containsa plurality of exits for the nitrogen stream and is located just belowscrew 36 and above grid 38, and which serves to ensure betterdistribution of nitrogen through the body of chips located above and ongrid 38. The nitrogen escapes to. the atmoing the drying operation. Ofcourse the amount of solid phase polymerization depends upon the chiptemperature such just beginning to occur with polyhexamethyleneadipamide at about 170 C. it should be understood, however, that thisinvention does not require any solid phase polymerization. j

Sufficient nitrogen must be provided to carry off enough water from thechips to shift the equilibrium in the meltto the desired RV.Thisincludes water in the chips fed to the tube heater and also thatwater of condensation which is produced in any, solid phasepolymerization which occurs in the tube. Moreover, condensation of waterfrom the nitrogen stream must be prevented in the upper, cooler portionof the tube and in the feed hopper. While an excess of nitrogen has noeffect on RV, a'shortage of'nitrogen will reduce the final RV bylimiting the amount of water which is removed from the chips..-

Drying temperature is a process control variable of secondary importancefor increasing the relative viscosity. 0f greater significance, becausethe diffusion of moisture to the chip surface is slow'and the chiptemperature must be kept below the melting point, is the residence timeof the chips in the tube heater during drying. Sufficient time must beallowed for diffusion of moisture to the chip surface whereby it can becarried away by the nitrogen purge stream. Merely by way of example, ata melter throughput of about lb. per hr., a residence time of about 27minutes is required in a tube 16 feet long wherein the chip temperature,measured as hereinafter disclosed, is about C. and the nitrogen flow is10 scfm to obtain a polymer of about 65 RV. Varying the heated length ofthe tube or the melter throughput changes the RV by altering theresidence time. If adequate residence time and nitrogen flow areavailable, and given adequate residence time there is no limit on RV,the heat input, i.e., the column temperature will control the degree ofdrying. Merely by way of example, a polymer of about 60 RV can beobtained when chips charged to the tube at a rate of from about 35 lb.per hr. to about 70 lbs. per hr., are heated for from about 60 min. toabout 30 min. at a temperature of from about 130 C. to about 170 C., thenitrogen flow being from about 4 scfm to about 8 scfm.

The final RV can be raised by increasing the Dowtherm temperature in themelter which increases the drying at and immediately above the grid.However, it should be pointed out that below a Dowtherm temperature ofabout 280 C. melt viscosity is too high, and that above temperatures ofabout 305 C. excessive gel and- /or thermal degradation results in themelt pool. Preferably, the melter is operated at a Dowtherm temperatureof from about 285 C. to about 290 C.

Feed hopper 10, into which is fed polymer chips for the feeding of tubepolymerizer 11, can be of any desired design so long as there ismaintained an adequate supply of chips to the tube heater. It can beopentopped, as shown in the drawing, and have a shape similar to acommon funnel. A valve means 13 which can be a simple slide orgate-valve, is located in the spout 14 thereof for preventingundesirable flow of chips, which may be in any desired amount, dependingon the relative viscosity desired in the final product, size of tube,i.e., tube inside diameter and tube length, melter capacity, residencetime, and the like, as will be understood by those skilled in the art,into tube 11. Valve means 13, as will be hereinafter more fullyunderstood, also allows for the escape of volatiles produced during thesubsequent drying operation, e.g. water vapor, and the inert gascarrier, nitrogen. Of critical concern, however, with respect to valvemeans 13 and spout 14 is the fact that bridging of chips must be avoidedin order that a constant and uniform supply of polymer chips bemaintained to tube 11.

Tube 11, into which polymer chips are fed for heating and drying can beof any desired length so long as adequate residence time is allowed atthe polymer throughput for the desired degree of heating and drying inorder that the desired relative viscosity increase will occur in thesubsequent melt polymerization. While in the particular embodiment shownin the drawing and described in the example hereinafter given the tubeheater comprises a plurality of elongated tubular sections joinedtogether in a conventional manner by flanges or the like there is noreason why it cannot be one continuous tube of the desired length.Providing the tube heater in sections, however, may present oneadvantage in that it can provide for a greater flexibility with respectto varying throughputs. Quite obviously,

of course, whether the desired residence time is attained for anyparticular length tube heater depends upon the polymer chip throughput.Throughput, or polymer chip feed for a given period of time depends, ofcourse, on the rate of use of the polymer, i.e., the rate of extrusion.It being highly desirable, of course, to melt chip at a ratesubstantially equal to that of the rate of extrusion, thereby keeping toa constant minimum period the exposure of the molten polymer totemperatures at which decomposition occurs. While residence time isdependent on tube length, other factors also of a critical nature aredependent on tube diameter. The inside diameter of tube heater 11 mustbe kept relatively small to insure plug flow and to keep the radialtemperature gradient to a minimum. While the inside diameter depends, ofcourse, to some extent on the polymer chip size, in conventionallyproduced irregular shaped chip passing through a as inch screen a tubehaving an inside diameter of from about 2 inches to about 6 inches issatisfactory. preferably, however, the tube is about 3- 1: inches insidediameter.

Heat, in the embodiment shown in the drawing, is supplied to thepolymer. chips in four separate and distinct heating zones l5, 16, 17and 18 by means of conventional electrical resistance strip heaters 19,20, 21 and 22 surrounding tube heater 11. While heat input is desirablyuniform around the circumference of the tube, it of course can besupplied by other heating means, e.g., steam, heated liquids, or thelike and need not be supplied in separate zones such as is shown in thedrawing. Tube 11 can, for example, be jacketed so as to provide forheating the tube walls by an appropriate heating fluid, such as steam orthe like. The heating elements and tube are enclosed in insulation 23.The heat supply to the polymer chips in each of the separate heatingzones is controlled by means of a separate temperature controller, ofconventional design, e.g. a Honeywell Versatronic, as is indicated inthe drawing by reference numerals 24, 25, 26 and 27. Polymer chiptemperature is determined by means of thermocouples 28, 29, 30, 31 and32 and the heat supply is regulated accordingly to maintain the desiredtemperature of chips feeding into chip melter 12. The degree of dryingof the chips is controlled by the chip temperature determined bythermocouple 31 which preferably is located at some distance from theend of tube 11 thereby providing amore uniform and better temperatureindication by avoiding such end effects as radiation and the like. Thistemperature is not only the measure of drying but also the measure ofpolymerization which will occur in the melter. It is of course essentialthat the heat input source, i.e., the tube wall be well below thepolymer chip melting temperature at all times which forpolyhexamethylene adipamide chip means that the tube wall is desirablyless than 245 C. to prevent chips sticking. I

From tube 11, the polymer chips pass through feed conduit 33, which isconnected to tube 11 by means of expansion joint 34, into chip melter12. The rate of flow of chips from tube 11 must be uniform to avoidvariations in residence time in the tube heater, thus avoiding varyingdegrees of polymerization in the the melt pool and a product ofnon-uniform quality and properties. Located in conduit 33 is a samplepoint 35 comrising an outlet with a valve therein. Samples of chipdischarging from the tube heater are obtained through the sample pointfor the determination of the degree of drying thereof and any attendantsolid phase polymerization. The chip melter 12 is jacketed and ofconventional design, being more fully described in US. Pat. No.3,010,147, the disclosure of which is incorporated herein by reference,having located therein screw feed means 36, which is rotated by means ofmotor 37, for feeding polymer chips into melter l2 and against a hotmetal grid 38 for melting. The grid 38, as is melt chamber 39, is heatedby Dowtherm heating fluid having a temperature of from about 280 C. toabout 305 C., preferably 285290 C. The polymer chips upon melting passthrough the interstices in grid 38, and flow down through downspout 40forming a body of molten polymer 41 in melt chamber 39. The moltenpolymer 41 is, while in the melt chamber, blanketed under inert gas,e.g., nitrogen introduced through inlet 42, and is stirred by means ofagitator 43 located therein. The

polymer after reaching equilibrium in the melt, i.e. 10

after about 4 minutes at a throughput of 70 lbs. per hr., to aspinnerette, not shown, by booster pump 44 for the formation ofcontinuous filaments, according to conventional spinning techniques.

By way of further illustration the invention will now be described inthe following examples wherein reference to parts or percentages thereinis intended to be by weight unless otherwise indicated.

EXAMPLE A 48percent aqueous solution of hexamethylene diammonium adipate(nylon 66 salt) which may be prepared in accordance with the proceduredisclosed in U.S. Pat. No. 2,130,947 is charged to a stainless steelevaporator, which has been purged previously of air with purifiednitrogen and is concentrated to 60perc'ent at atmospheric pressure,which corresponds to a final temperature of about 105 C. The 60 percentsalt solution is transferred from the evaporator which is so positionedthat the content thereof can be transferred when reaches 250 psi. Uponreaching 250 psi, steam is gradually bled off through appropriate meansand such pressure is maintained and the heating is continued until theconcentration of the salt is about 90 percent (temperature isapproximately 230 C.) Heating and bleeding of steam at 250 psi pressureare continued until the temperature reaches 245 C. whereupon thepressure is gradually reduced by accelerating the steam bleedoff for aperiod of 90 minutes, until the temperature has reached 270 C.-and thepressure has been reduced to atmospheric. Heating at atmosphericpressure is continued until 275 C. is reached to complete thepolymerization. The autoclave is brought to 100 psi by the introductionof an oxygen-free gas (e.g., nitrogen) and molten polymer is dischargedas a ribbonas shown in the last-mentioned patent, by extrusion through anarrow slit in the discharge head at the bottom of the autoclave. Theribbon is quenched by well-known means such as on a water-cooled castingwheel and cut or broken up into chips by passing the ribbon through acutting apparatus. The chips are collected in appropriate containers fortransfer to the apparatus of this invention.

The chips of vpolyhexamethylene adipamide polymer produced asabove-describedand having an RV measured, as before described, of 49 andcontaining from about 0.5 1.0 percent H O'are forwarded at 69.4 lbs. perhr. to tube heater 11 via feed hopper 10 as previously described. Thetube heater is made up of four 4 tubular sections joined togethere'nd-to-end having an internal diameter of 3- /4 inches and an outsidediameter of 3-% inches. Eight Chromalux electrical strip heaters eachbeing 4 X 1-95" are positioned on the tube in pairs. Each successivepair is positioned to that of the adjacent pair, and are maintained at190 C., 205 C., 205 C. and 205 C. The lower temperature corresponds tothe strip heaters located in the upper tubular section, i.e. the sectioninto which chips are fed from hopper 10. Nitrogen at room temperature,i.e. about 22 C., and in an amount of l0scfm having an analysis lessthan about 5 parts per million oxygen and 10 parts per million water isintroduced into melter 12 by way of conduit 44 and the circularmanifold, previously mentioned. The nitrogen is well distributedthroughout the mass of chips located above and on melt grid 38 andpasses up the tube heater ll countercurrent to chip flow. The chiptemperature indicated by thermocouple 31 located about four feet fromthe tube exit and about '/z inch in the chip mass is controlled with thestrip heaters at the above-indicated temepratures at 172 C. to insure anadequate degree of drying of the chips. The chips pass through conduit33 into melter 12 and are melted on'melt grid 38 maintained at aDowtherm temperature of 291 C. The polymer melt has a final RV of 65. Amelt pool of about'4i4 lbs of molten polymer is maintained in the bottomof the melter providing a residencetime in the melter of about 4minutes. The melt pool is maintained under a blanket of nitrogen, thenitrogen being introduced'separately into an opening 42 near agitator43. This nitrogen escapes out through the openingsurrounding theagitator shaft. Molten polymer is supplied bybooster pump 44 at apolymer throughput of 69 lbs. per hr. to 4 spinnerette packs forspinning into filaments.

EXAMPLES 2 8 The process of Example 1 is repeated with processconditions varied as indicated in the table below. The molten polymericmaterial is extruded through a spinnerette having orifices therein of0.030 inches diameter. The filaments after having lubricant appliedthereto are collected together and wound into apackage at 960 feet perminute according to usual technique. The packaged yarn, in the case ofExamples-6 8, is then drawn at the draw ratio indicated to provide afinal denier of about 860. Yarn,properties on these samples are obtainedaccording to conventionaltechniques.

As can be determined from the data, among other Nylon 66 Relativeviscosity Yarn properties through Chip Melter put, lbs./ N; flow, N,temp, temp dowtherrn Entry Exit Extruded Draw Tenae- Elongahr. s.c.t.m.C." temp.,C. chip chip yarn ratio ity tion Modulus 35 2 183 291 48 51 7010 Not heated.. 153 303 48 49 70 do 291 48 49 70 10 .....do 178 291 4850 70 15 .d0 121 297 48.6 XXX 70 15 do 161 297 49.7 70 15 ..do 182 29750.2

Nitrogen temperature before entry into system.

Chip temperature taken at a point about length of tube from top(thermocouple indicated by reference numberai 81).

NOTE.XXX=N01; determined.

1 1 things, with increased chip temperatures one obtains increased meltpolymerization.

Filamentary yarn produced from the high relative viscosity polyamide ofthis invention finds particular utility for use as tire yarn. The yarnsfind ultility also in carpet and other textile uses.

While the invention is described herein with greater particularity withrespect to nylon 66, it is of course understood by those skilled in thepolymer art that such is applicable not only to other polyamides butalso to other linear condensation polymers, e.g. polyesters, or mixturesof polyamides or polyamide-polyester. Moreover, it'is also deemed quiteobvious to those skilled in the art that use of the tube polymerizer isnot restricted to grid melters. A screw extruder, for example, can beused in place of a grid melter with similar effect. If vertical space isa problem, multiple tubes, or altered tube cross-sectional shapes can beused so long as plug flow is maintained, the radial heat gradient iskept small, and chip bridging at the tube outlet to the melter isavoided.

Furthermore the apparatus has utility as a drier, eg in the drying ofpolyester or polycaprolactum chips without increasing the relativeviscosity thereof.

It should also be pointed out that the invention is not limited to theproduction of polymeric material of high relative viscosity, i.e., above50 RV. It is equally applicable to increasing the RV in polymericmaterial of any relative viscosity and finds particular utility informing textile grade polymeric material of good uniformity. Theinvention will allow for more efficient and effective use ofconventional autoclaves. Polymerization in the autoclave can be carriedon to a-lower RV level thereby resulting in less gel formation, easierand faster discharge of polymer from the autoclave, thus resulting inpolymer of more uniform RV and better physical properties, and a reducedautoclave cycle time with attendant increased productivity.

It is understood that the foregoing detailed description is given merelyby way of illustration and that many variations may be made thereinwithout departing from the spirit of my invention.

1 claim:

1. An apparatus for the preparation of filamentary material fromthermoplastic polymer chip, said apparatus comprising a substantiallyvertically disposed heating tube having electrical strip heaters andhaving a passageway extending therethrough, a hopper for enteringpolymer chip into the top of said passageway, a valve means disposedintermediate said hopper and said heating tube, a melter operativelyconnected to the bottom of said heating tube but out of axial alignmentscrew feed means and said melt chamber.

* t l l t

2. The apparatus of claim 1 wherein said melter has a melt chamber belowsaid feed screw means and a chip receiving melt grid member disposedintermediate said screw feed means and said melt chamber.